Gastro-entero-pancreatic hormonal and metabolic responses to bicycle ergometer exercise for one hour following twelve hours fasting (P1) and 36 hours fasting (P2) were compared. During P1 plasma secretin and blood glycerol increased. Pre-exercise concentrations of plasma C-terminal glucagon-like-immunoreactivity (C-GLI), secretin, blood glycerol, 3-hydroxybutyrate and lactate were higher after 36 hours fasting than 12 hours fasting. During P2 glycerol rose sharply while secretin, C-GLI and 3-hydroxybutyrate remained higher than during P1. A role for secretin and C-GLI in accelerated lipolysis during fasting and exercise is possible.